Secondary fuse



March 22, 1938n E. F. BOOTHE 2,111,745

SECONDARY FUSE Filed Dec. 14, 1936 jig. J Jg@ 2 1;#9. J

//y VEN TOR,

A TTO/B/YEY Patented Mar. 22, 1938' UNITED STATES PATENT OFFICE James R.

Kearney Corporation,

St. Louis,

Mo., a corporation of Missouri Application December 14, 1936, Serial No.115,652

9 Claims.

This invention relates generally to secondary fuses and morespecifically to a. fuse of this Vtype which includes expansible springmeans adapted on rupture of the fusible link of the fuse to quicklyseparate the ruptured ends of said fusible link so as to extinguish thearc, the predominant object of the invention being to provide a fuse ofthis improved construction and amusement ,which in addition toperforming its intended function in an improved and highly efficientmanner indicates, by the positions of certain of its parts whether ornot the fuse has been blown.

As is generally known by persons familiar with the distribution ofelectrical energy practically every system of overhead secondary inurban districts consists of a network or grid, minus the actualinterconnections between individual transformer sections. 'In generalthe gaps between transformer sections consist of strain insulatorsinserted in the outer wires of the three-wire sec-3 secondary fuses maybe arranged in each live l leg of each transformer secondary. Also insome cases a combination of these two methods is ernployed. Additionallyin most cases secondary fuses` are inserted in service taps which supplyunusuallyheavy service and those installed in conduits extended down apole and leading underground to a consumers premises.

Because of a demand for a secondary fuse which is capable of performingits intended function in a highly eilicient manner I have devised theimproved fuse structure disclosed herein, the

' predominant feature of which is that an expan- `sible coil spring isincorporated in the fuse structure in such manner that the ruptured endsoi the fusible element of the fuse are quickly pulled apart when thefusible element blows. Also because ofthe use of this coil spring a partof the fuse strcture and a part of thecoil spring are moved to suchoutwardly extended positions when the fuse blows as to readily indicateto a person inspecting the fuse structure that the fusible Clementthereof has been ruptured.

(Cl. 20o-117) Fig. l is a view illustrating one manner of use of theimproved secondary fuse.

Fig. 2 is a sectional-elevation of the improved secondary fuseshowing'same in an unblown condition.

Fig. 3 is a view similar to Fig. 2, but showing the fuse illustratedtherein in a blown condition.

Fig. 4 is an enlarged fragmentary sectional View of a portion of theimproved fuse.

Fig. 5 is an enlarged cross-section on line 5-5 of Fig. 2.

Fig. 6 is an enlarged cross-section on line 6 6 of Fig. 2.

In the drawing, wherein is shown for the purpose of illustration,merely, oneembodiment of the invention, A designates the improvedsecondary fuse generally. The fuse A comprises a pairof cables i and 2which serve as fuse terminals, said cables being spaced apart at theiradjacent inner ends to provide a gap as shown to the best advantage inFig. 2. When the improved secondary fuse is in its normal unblowncondition as shown in Fig. 2, the spaced apart inner end portions of thecables i and 2 are joined by a fusible element 3 which is provided atits opposite ends with clamping means l and 5 adapted to be securelyclamped or crimped to said end portions of the cables so as tomechanically and electrically connect the cables together. The clampingmeans 4 and 5 comprise each a piece of bendable metal having portionsadapted to be bent into embracing relation with respect to theassociated cable as shown in Figs. 2, 5, and 6, and' the fusible element3 is soldered or otherwise secured at its opposite ends to said clampingmeans.

Secured to the cable l is a tube retaining element l which comprises anintermediate annular flange 'l' from which is extended outwardly asleeve portion the metal of which is thin enough to be pliable. Extendedin the opposite direction from the intermediate ilange 'l is a collar 9which is of less diameter than said intermediate flange. Also the tuberetaining element 6 includes a centrally apertured disk ill, the reducedinner portion of the sleeve portion 8 being extended through theaperture of the disk and the portion of the disk surrounding theaperture being confined between the larger portion of the sleeve portionand the intermediate flange 1. 'I'he tube retaining element 6 isprovided with an opening formed entirely therethrough and the cable I isextended through said opening, said tube retaining element being securedto said cable by having the sleeve 8 crimped into tight frictionalengagement therewith.

'Ihe improved secondary fuse includes a tube II formed of Bakelite orother suitable weatherresisting material which at one of its endscontacts with the disk I0 and embraces the intermediate annular ilange 1of the tube retaining element, the inner face of said tube II at saidend thereof being in close contact with the peripheral face of saidintermediate annular flange. Arranged within the tube II is a secondtube I2 which is formed of horn fibre or other suitable materialcharacterized by the ability to give oil.r a gas in the presence of anelectric are that tends to extinguish said electric arc. The tubes I Iand I2 terminate in alinement at one end of the combined tube structureas shown 'in Figs. 2 and 3 and at this end of said tube structure thetubes are secured together and to the cable 2 by a pin I3 which extendsthrough apertures formed through the walls of the tubes II and i2 andthrough apertures formed through the clamping means 5 and the cable 2.

Arranged in embracing relation with respect to the inner portion of thecable I is a coil spring I4. One end of the coil spring I4 is attachedto the tube retaining element 6 by having an end portion I4a thereofextended into an opening formed in the collar 9 of said tube retainingelement, and the opposite end of said coil spring is attached to theinner tube I2 by having an end portion IIb of the coil spring insertedin an aperture formed in the wall of said inner tube. By referring toFigs. 2, 3, and 4 it will be noted that the inner tube I2 is of lesslength than the outer tube II to provide a space I5 in which the coilspring I4 is located. Also the relative diameters of the tubes II and I2are such that a space I6 is present at one side of the tube structurebetween the walls of said tubes which permits a portion of the coilspring adjacent to the portion Mb thereof to extend between said wallsof the tubes II and I2.

In the normal unblown condition of the improved secondary fuse the coilspring is compressed as shown in Fig. 2 and to retain said coil springin such condition and eliminate imposition of mechanical strain createdby the contracted coil spring on the fusible element 3 a strain wire I1is provided. The strain wire is suitably secured at its opposite ends toextensions II of the clamping means 4 and 5 and is of sumcient strengthto hold the coil spring in its retracted condition.

When in the use of the improved secondary fuse abnormal passage ofcurrent therethrough occurs, the fusible element 3 is ruptured and theresultant electric arc immediately severs the strain wire I1. This freesthe contracted coil spring I4 from restraint and said coil springexpands quickly and forcibly to the position shown in Fig. 3 therebydrawing the rupturedends of the fusible element and the strain wireapart to extinguish the electric arc, such extinguishment of theelectric arc being aided by a gas formed when the inner horn fibre tubeI2 is subjected to the heat of the electric arc. It is to be noted thatthe opposite ends of the coil spring are attached to the cable I throughthe tube retaining element 6 and to the cable 2 through the inner tubeI2, hence the separated parts of the fuse structure do not y entirelyapart when the fuse blows but are held together in a separated conditionby the coil spring. Also when the improved fuse has been blown a part ofthe coil spring and the tube retaining element are projected aconsiderable distance beyond the adjacent end of the tube l I to providea visual indication that the fuse has blown.

In Fig. 1 I illustrate a typical installation involving the use ofsecondary fuses of the type disclosed herein. In this view B designatesa transformer supported by a suitable element such as a crossarm of apole, which transformer is electrically connected to power lines C by atransformer secondary D. The installation illustrated includes secondaryfuses F and F' in the live legs of the transformer secondary, thesecondary fuse F' being illustrated in the blown condition.

I claim:-

1. A secondary fuse comprising terminal cables spaced apart at theirinner adjacent ends to provide a gap, a fusible element bridging saidgap and electrically connected at its opposite ends to said terminalcables, an expansible coil spring arranged in a contracted condition andadapted on rupture of said fusible element to expand and draw theruptured ends of said fusible element apart, and a tube enclosing saidfusible element, said coil spring and inner portions of said terminalcables when the fuse is in an unblown condition, said coil spring beingmaintained in a position where a portion thereof is extended from an endof said tube when the fusible element has been ruptured so as toindicate the blown condition of the fuse.

2. A secondary fuse comprising terminal cables spaced apart at theirinner` adjacent ends to provide a gap, a fusible element bridging saidgap and electrically connected at its opposite ends to said terminalcables, a strain wire connected to and extended between the inneradjacent ends of said terminal cables. an expansible coil springarranged in a contracted condition and adapted on rupture of saidfusible element to expand and draw the ruptured ends of said fusibleelement apart, and a tube surrounding said fusible element, said coilspring and inner portions of said terminal cables, said coil springbeing maintained in a position where a portion thereof is extended froman end of said tube when the fusible element has been ruptured so as toindicate the blown condition of the fuse.

3. A secondary fuse comprising terminal cables spaced apart at theirinner adjacent ends to provide a gap, a fusible element bridging saidygap and electrically connected at its opposite ends to said terminalcables, .a strain wire connected to and extended between the inneradiacent ends of said terminal cables, an expansible coil springarranged in a contracted condition and adapted on rupture of saidfusible element to expand and draw the ruptured ends of said fusibleelement apart, a tube surrounding said fusible element and said coilspring, a tube retaining element mounted on one of said terminal cablesand adapted to engage an end of said tube, e

and means for attaching the opposite end of the tube to the other ofsaid terminal cables, said coil spring being maintained in a positionwhere a portion thereof is extended from an end of said tube when thefusible element has been ruptured so as to indicate the blown conditionof the fuse.

4. A secondary fuse comprising terminal cables spaced apart at theirinner adjacent ends to provide a gap, a fusible element bridging saidgap and electrically connected at its opposite ends to said terminalcables, a strain wire connected to and extended between the inneradjacent ends of said terminal cables, an expansible coil springarranged in a contracted condition and adapted on rupture of saidfusible element to expand and draw the ruptured ends of said fusibleelement apart, a tube surrounding said fusible element and said coilspring, a tube retaining element mounted on one of said terminal cablesand adapted to releasably engage an end of said tube, and means forattaching the opposite end of the tube to the other of said terminalcables, said coil spring being maintained in a position where a portionthereof is extended from an end of said tube when the fusible elementhas been ruptured so as to indicate the blown condition of the fuse.

5. A secondary fuse comprising terminal cables spaced apart at theirinner adjacent ends to provide a gap, a fusible element bridging saidgap and electrically connected at its opposite ends to said terminalcables, an expansible coil spring arranged in a contracted condition andadapted on rupture of said fusible element to expand and draw theruptured ends of said fusible element apart, an outer tube surroundingsaid fusible element and said coil spring, and an inner tube within saidouter tube which surrounds said fusible element, said inner tube beingformed of material characterized by the ability to give off a gas whensubjected to the heat of an electric are which tends to extinguish saidelectric arc, said coil spring being maintained in a position where aportion thereof is extended from an end of said outer tube when thefusible element is ruptured so as to indicate the blown condition of thefuse.

6. A secondary fuse comprising terminal cables spaced apart at theirinner adjacent ends to provire a gap, a fusible element bridging saidgap and electrically connected at its opposite ends to said terminalcables, a strain wire connected to and extended between the inneradjacent ends of said terminal Icables, an expansible coil springarranged in a contracted condition and adapted on rupture of saidfusible element to expand and draw the ruptured ends of said fusibleelement apart, an outer tube surrounding said fusible element and saidcoil spring, and an inner tube within said outer tube which surroundssaid fusible element, said inner tube being formed of materialcharacterized by the ability to give off a gas when subjected to theheat of an electric arc which tends to extinguish said electric arc,said coil spring being maintained in a positionwherea portion thereof isextended from an end of said outer tube when the fusible element isruptured so as to indicate the blown condition of the fuse.

'7. A secondary fuse comprising terminal cables spaced apart at theirinner adjacent ends to provide a gap, a fusible element bridging saidgap and electrically connected at its opposite ends to said terminalcables, a strain wire connected to and extended between the inneradjacent ends of said terminal cables, an expansible coil springarranged in a contracted condition and adapted on rupture of saidfusible element to expand and draw the ruptured ends of said fusibleelement apart, an outer tube surrounding said fusible element and saidcoil spring, and an inner tube within said outer tube which surroundssaid fusible element, said inner tube being formed of materialcharacterized by the ability to give ofi! a gas when subjected to theheat of an electric arc which tends to extinguish said electric arc,said coil spring being connected at one of its ends to one of saidterminal cables and at its opposite end to said inner tube whereby it ismaintained in a position where a portion thereof is extended from an endof said outer tube when the fusible element is ruptured so as toindicate the blown condition of the fuse.

8. A secondary fuse comprising terminal cables spaced apart at theirinner adjacent ends to provide a gap, a fusible element bridging saidgap and electrically connected at its opposite ends to said terminalcables, a strain wire connected to and extended between the inneradjacent ends of said terminal cables, an expansible coil springarranged in a contracted conditionA and adapted on rupture of saidfusible element to expand and draw the ruptured ends of said fusibleelement apart, an outer tube surrounding said fusible element and saidcoil spring, a tube retaining element mounted on one of said terminalcables and adapted to engage an end of said outer tube, an inner tubelocated within said outer tube and characterized by the ability to giveoff a gas when subjected rc the heat of an electric arc which tends toextinguish said electric arc, said coil spring being connected at one ofits ends to said tube retaining element and at its opposite end to saidinner tube whereby it is maintained in a position where a portionthereof is extended from an end of said outer tube when the fusibleelement is ruptured so as to indicate the blown condition of the fuse,and means for attaching the outer and inner tubes to the terminal cableopposite to the terminal cable on which said tube retaining element ismounted.

9. A secondary fuse comprising terminal cables spaced apart at theirinner adjacent ends to provide a gap, a fusible element bridging saidgap and electrically connected at its opposite ends to said terminalcables, a strain wire connected to and extended between the inneradjacent ends of `said terminal cables, an expansible coil springarranged in a contracted condition and adapted on rupture of saidfusible element to expand and draw the ruptured ends of said fusibleelement apart, an outer tube surrounding said fusible element and saidcoil spring, a tube retaining element mounted on one of said terminalcables and adapted to releasably engage an end of said outer tube, aninner tube located Within said outer tube and characterized by theability to give off a gas when subjected to the heat of an electric arcwhich tends to extinguish said electric arc, said coil spring beingconnected at one of its ends to said tube retaining element and at itsopposite end to said inner tube whereby it is maintained in a positionwhere a portion thereof is extended from an end of said outer tube when,the fusible element is ruptured so as to indicate the blown conditionof the fuse, and means for attaching the outer and inner tubes to theterminal cable opposite to the terminal cable on which said tuberetaining element is mounted.

1 'EUGENE F. BOOTHE.

